Effective detection of one or more flaws in vehicles, such as rolling stock components in the rail industry, or commercial trucks, is highly desirable. For example, detection of flaws or problems with the wheels, brake components (including drums, discs, etc.), electronic brake control systems, air conditioning units, transmission, driving motors, and/or the like, is desirable so that corrective action can be taken, e.g., to prevent a derailment, highway accident, further damage, fire, or the like.
Current detectors include detectors that attempt to detect bearing overheating (e.g., hot box detectors) and detectors that attempt to detect brake/wheel component overheating (e.g., hot wheel detectors). The rail industry has utilized hotbox detectors for over fifty years to detect overheating bearings and thereby prevent derailment. These thermal detectors are mounted on the rail or in close proximity to the rail to provide hot bearing and hot wheel data.
Measurements made with such single element detectors are subject to large errors due to variations in emissivity of bearing and wheel radiating surfaces. The infrared detectors typically used, such as thermoelectric, thermistor bolometer and pyroelectric detectors, also usually are limited to monitoring lower speed vehicles, e.g., vehicles typically traveling under one hundred fifty kilometers per hour. However, higher speed trains in use in Europe can travel as fast as four hundred fifty kilometers per hour.
Currently used thermal detectors monitor radiation in the long wave infrared (LWIR) region, e.g., having wavelengths between eight and fourteen microns. Thermal detectors are inherently slow as infrared absorption is followed by heating of the detector element mass. Heating of the detector element results in a physical property change, e.g., resistance change for the thermistor bolometer. An additional issue with existing rail mounted hot box detectors is microphonic noise generated by the pyroelectric detections in response to rail shock and vibration. Other difficulties with the use of conventional hot box and hot wheel detectors are the relative high cost of LWIR optics fabricated from germanium or special long wave infrared glasses, and the considerable motion induced blurring conspicuous with vehicles moving at higher operating speeds.
Previous approaches have proposed using arrays of pyroelectric detectors and thermopiles for hot wheel and hot bearing detection. For example, one approach includes a hot wheel detector that utilizes an eight element linear array of pyroelectric detectors. Another approach uses a vacuum packed micro thermopile (thermoelectric) array for wheel and bearing monitoring. However, these array detectors suffer from many of the drawbacks listed above regarding the use of conventional bolometer type thermal detectors in the LWIR region for hot wheel and hot bearing detection.